In heat-set blow molding machines, e.g. for PET bottles for beverages to be filled in a hot state, the molds are additionally heated up by temperature control devices with a heat carrier medium to a heat-set operating temperature. For converting the heat-set blow molding machine to a different type of bottle the molds must be exchanged. A heat-set blow molding machine contains, for example, at least eight molds, or up to thirty molds or more. The heat-set operating temperature may be about 130° C. to 180° C., so that upon a mold change one must first wait until the molds have cooled down to a handling temperature of e.g. 40-60° C. Although the molds are cooled by the further conveyed and no longer heated heat-carrier medium of the temperature control devices, it takes at least about half an hour until the molds have cooled down to about 60° C. and can be exchanged, and more than one hour until the molds have cooled down to about 40° C. and can be exchanged. A mold change is therefore tantamount to a high production loss. If stretch blow molding is carried out in the heat-set blow-molding machine, a stretch type purge rod or stretching rod is introduced into each mold; the rod mechanically pre-stretches the preform in the mold during a normal work cycle and supplies the blow air over a defined portion of the normal work cycle so as to bring the pre-stretched preform into the bottle form. Optionally, before the bottle is removed from the mold, purge air is also blown in for a short period so as to be able to remove the bottle in a dimensionally stable manner. As a rule, however, every mold is cooled in preparation of a change only by the still circulating and no longer heated heat carrier of the temperature control devices.
It is known from JP 3222714 that for a faster solidification of a molding in a mold and for shortening the cycle time heating is first carried out with gas, and then cooling.
It is known from JP 9085420 A that a metal mold is cooled with cooling water during the molding operation.
It is known from U.S. Pat. No. 6,991,756 B1 that a heat-exchange apparatus is internally assigned to a metal mold so as to guide either a liquid, hot or cold heat carrier through heat exchange passages of the mold and to purge the respective heat carrier with purge air during transition from the hot to the cold heat carrier.
Finally, it is known from DE 4242024 C2 that a mold for plastic processing is held with a liquid at operating temperature in channels separated from the mold cavity and to solidify plasticized plastics introduced at an elevated temperature and to remove liquid contained in the channels with compressed air prior to a mold change.